1. Field of the Invention
The present invention relates to a scroll type fluid displacement apparatus, and more particularly, to an improvement in the rotation preventing mechanism in a scroll type fluid displacement apparatus.
2. Description of the Prior Art
A scroll type fluid displacement apparatus is well known in the prior art. For example, U.S. Pat. No. 4,892,469 issued to McCullough discloses a basic construction of a scroll type fluid displacement apparatus.
Referring to FIGS. 1, 2 and 3, a scroll type fluid displacement apparatus in accordance with the prior art is shown in the form of scroll type refrigerant compressor unit 1. Throughout this description the terms "front" and "rear" are used to assist in the description. These terms are in no way intended to limit the description. With reference to FIG. 1, the left of the figure is referred to as the "front" and the right as the "rear." Compressor unit 1 includes housing 10 having front end plate 11 and cup shaped casing 12 which is attached to an end surface of front end plate 11. Opening 111 is formed in the center of front end plate 11 for the penetration of drive shaft 13. Annular projection 112 is formed in the rear end surface of front end plate 11 and is concentric with opening 111. An outer peripheral surface of annular projection 112 extends into cup shaped casing 12. Thus, the open end of cup shaped casing 12 is covered by front end plate 11. O-ring 14 is placed between the outer peripheral surface of annular projection 112 and the inner wall of the open end of cup shaped casing 12 to seal the mating surfaces therebetween.
Front end plate 11 has an annular sleeve 15 projecting from the front end surface thereof. Annular sleeve 15 surrounds drive shaft 13 and forms shaft seal cavity 60. Annular sleeve 15 is formed separately from front end plate 11, and is attached to the front end surface of front end plate 11 by screws (not shown). O-ring 16 is placed between the front end surface of front end plate 11 and rear end surface of sleeve 15 to seal the mating surfaces therebetween. Alternatively, sleeve 15 may be formed integrally with front end plate 11.
Drive shaft 13 is rotatably supported by annular sleeve 15 through bearing 17 located near the front end of annular sleeve 15. Drive shaft 13 has a disk portion 18 at its inner end portion which is rotatably supported by front end plate 11 through bearing 19 located within opening 111. Shaft seal assembly 20 is coupled to drive shaft 13 within shaft seal cavity 60.
Pulley 21 is rotatably supported by bearing 22 which is disposed on the outer surface of sleeve 15. Electromagnetic coil 23 is fixed around the outer surface of sleeve 15 by support plate 24 and is received in an annular cavity 61 of pulley 21. Armature plate 25 is elastically supported on the outer end of drive shaft 13. Pulley 21, magnetic coil 23 and armature plate 25 form magnetic clutch 62. In operation, drive shaft 13 is driven by an external power force, for example the engine of the automobile, through a rotational force transmitting device, such as magnetic clutch 62.
A number of elements are located within the inner chamber of cup shaped casing 12, including fixed scroll 26, orbiting scroll 27, a driving mechanism for orbiting scroll 27 and rotation prevention/thrust bearing device 37 for orbiting scroll 27. The inner chamber of cup shaped casing 12 is formed between the inner wall of cup of shaped casing 12 and the rear end surface of front end plate 11.
Fixed scroll 26 includes circular end plate 261, wrap or spiral element 262 affixed to or extending from one end surface of end plate 261 and a plurality of internally threaded bosses 263 axially projecting from the other end surface of circular end plate 261. Fixed scroll 26 is secured within the inner chamber of cup shaped casing 12 by screws 28, which screw into internally threaded bosses 263, from outside of cup shaped casing 12. Circular end plate 261 of fixed scroll 26 partitions the inner chamber of cup shaped casing 12 into front chamber 29 and rear chamber 30. Seal ring 31 is disposed within a circumferential groove in circular end plate 261 to form a seal between the inner wall of cup shaped casing 12 and the outer surface of circular end plate 261. A hole or discharge port 264 is formed through circular end plate 261 at a position near the center of spiral element 262. Discharge port 264 creates fluid communication between the central fluid pockets of spiral element 262 and rear chamber 30.
Orbiting scroll 27, which is located in front chamber 29, includes circular end plate 271 and wrap or spiral element 272 affixed to or extending from one end surface of circular end plate 271. Orbiting scroll 27 is supported by bushing 34 through bearing 35 placed between the outer peripheral surface of bushing 34 and an inner surface of annular boss 273 axially projecting from the front end surface of circular end plate 271. Bushing 34 is rotatably connected to the inner end of disk 18 at a point radially offset or eccentric to the axis of drive shaft 13. Drive shaft 13, which is rotatably supported by annular sleeve 15 through ball bearing 17, is integrally formed with disk 18. Disk 18 is rotatably supported by front end plate 11 through ball bearing 19 disposed within opening 111. Drive pin 41 projects axially from the rear end surface of disk 18 and is radially offset from the center of drive shaft 13. Bushing 34 is rotatably secured to drive pin 41 by snap ring 44.
Bushing 34 has balance weight 341, which is shaped as a disc or ring, extending radially along a front surface thereof. Balance weight 341 is secured to the front surface of bushing 34 by rivets 46 (FIG. 2), and generates a centrifugal force that opposes the centrifugal force generated by orbiting scroll 27. The centrifugal force generated by balance weight 341 is slightly higher than the centrifugal force due to the orbital motion of orbiting scroll 27 and the parts orbiting with it. Balance weight 341 has weight member 342 shaped as an arc (FIG. 2) and secured thereto by rivets 47. Balance weight 341 is accommodated in a hollow portion 50 which is formed between front end plate 11, bearing 19, disk 18 and annular boss 273. Eccentric hole 44 (FIG. 2) and balanced hole 42 are formed in bushing 34 at a position radially offset from the center of bushing 34. Drive pin 41 fits into eccentric hole 44 within which a bearing (not shown ) may be applied. Bushing 34 is therefore driven in an orbital path by drive pin 41 and can rotate within needle bearing 35. Bushing 34 thus functions as a linkage member to drivingly connect orbiting scroll 27 to drive shaft 13 and drive pin 41.
A rotation preventing/thrust bearing device 37, which is disposed around annular boss 273, is operatively coupled to orbiting scroll 27. Orbiting scroll 27 is permitted to orbit without rotating, thereby compressing fluid passing through the compressor unit.
More specifically, spiral element 272 of orbiting scroll 27 is radially offset from the spiral element 262 of fixed scroll 26. Orbiting scroll 27 undergoes orbital motion upon the rotation of drive shaft 13. As orbiting scroll 27 orbits, spiral elements 262 and 272 remain in contact. The fluid pockets, which are defined between spiral elements 262 and 272, move to the center with consequent reduction in volume and compression of the fluid in the fluid pockets. The fluid or refrigerant gas which is introduced into front chamber 29 through inlet port 31, is taken into the outer fluid pockets formed between spiral elements 262, 272. As orbiting scroll 27 orbits, the fluid is compressed and finally discharged into rear chamber 30 through discharge port 264. The fluid then exits the compressor through outlet port 32.
Rotation preventing/thrust bearing device 37 includes a fixed portion, an orbital portion and bearings, such as a plurality of balls 377. Fixed portion includes annular race 371 placed within an annular groove formed on the axial rear end surface of annular projection 112 and fixed ring 372 which is formed separate from annular race 371 and fitted against the axial rear end surface of annular projection 112. Fixed ring 372 is secured to the axial rear end surface of annular projection 112 by pins 373 and covers the end surface of fixed race 371. The orbital portion of rotation preventing/thrust bearing device 37 includes an annular orbital race 374 placed within an annular groove formed on the front surface of end plate 271 and an orbital ring 375 which is formed separately from orbital race 374 and fitted against the front surface of orbital race 374. Orbital ring 375 is fixed on circular end plate 271 by pins 376 and radially extends beyond the front outer radial end surface of orbital race 374.
Fixed ring 372 and orbital ring 375 each have a plurality of holes or pockets 372a and 375a. Pockets 372a within fixed ring 372 correspond in location to pockets 375a within orbiting ring 375 so that at least each pair of pockets facing each other have the same pitch, and the radial distance of the pockets from the center of their respectively rings 372 and 375 is the same. The center of pocket 372a is offset from the center of pocket 375a by an amount equal to the radius of the pockets. Balls 377 are placed between the edge of pockets 372a of fixed ring 372 and the edge of pockets 375a of orbital ring 375.
During the operation of the scroll type compressor, balls 377 roll along the edge of pockets 372a, 375a. Thus, rotating motion of orbiting scroll 27 is prevented while its angular relationship with fixed scroll 26 is maintained.
Rotation preventing/thrust bearing device 37 typically includes a large number of balls 377. This is desirable so that the thrust load from the orbiting scroll is adequately absorbed. In the assembly process of the compressor, each of balls 377 must be placed between respective pockets 372a and 375a, during which balls 377 sometimes roll or are accidentally dropped into hollow portion 50. When this happens, a worker assembling the compressor often cannot detect such misassemblies. One solution is to design the compressor so that the axial length A (FIG. 3) is smaller than the diameter D of balls 377. When so designed, the front end plate 11 and orbiting scroll 27 will be misaligned if joined when a ball or balls 377 have fallen into hollow portion 50.
The misalignment, however, is extremely small. Consequently, the worker sometimes fails to detect the misassembly and proceeds to the next step of the assembly process. Furthermore, the relationship between axial length A and diameter D must be accurately determined, which in turn increases the manufacturing costs. Finally, sometimes it is necessary to modify the size and weight of the balance weight depending on the particular scroll configuration. Such modifications will necessarily have to take into account any changes made to axial length A and diameter D, thereby complicating design changes.